Processes of fermentation production of chemical products using sugars as raw materials have been used for producing various industrial materials. At present, as the sugars to be used as fermentation feedstocks, those derived from food materials such as sugar cane, starch and sugar beet are industrially used. However, in view of the fact that rise in the prices of food materials due to future increase in the world population is expected, or in an ethical view of the fact that sugars as industrial materials may compete with sugars for food, a process for efficiently producing a sugar liquid from a renewable nonfood resource, that is, a cellulose-containing biomass, or a process for using an obtained sugar liquid as a fermentation feedstock to efficiently convert the sugar liquid to an industrial material needs to be constructed in the future.
Examples of disclosed methods for producing a sugar liquid from a cellulose-containing biomass include methods for producing sugar liquids by acid hydrolysis of cellulose and hemicellulose using concentrated sulfuric acid (Japanese Translated PCT Patent Application Laid-open No. 11-506934 and JP 2005-229821 A) and a method wherein a cellulose-containing biomass is subjected to hydrolysis treatment using dilute sulfuric acid and then enzymatically treated with cellulase or the like to produce a sugar liquid (A. Aden et al., “Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover,” NREL Technical Report (2002)). Further, examples of disclosed methods using no acid include a method wherein a cellulose-containing biomass is hydrolyzed using subcritical water at about 250° C. to 500° C. to produce a sugar liquid (JP 2003-212888 A), a method wherein a cellulose-containing biomass is subjected to subcritical water treatment and then enzymatically treated to produce a sugar liquid (JP 2001-95598 A), and a method wherein a cellulose-containing biomass is subjected to hydrolysis treatment with pressurized hot water at 240° C. to 280° C. and then enzymatically treated to produce a sugar liquid (JP 3041380 B).
In recent years, methods of hydrolysis of a biomass which use less energy and cause less environmental load, but produce sugar at high yields have been extensively studied. However, such methods using enzymes have a drawback in that the costs of enzymes are high.
To solve these technical problems, methods of recovering and reusing the enzymes used in the hydrolysis have been proposed. Examples of such methods include a method wherein continuous solid-liquid separation is carried out with a spin filter and the obtained sugar liquid is filtered through an ultrafiltration membrane to recover the enzymes (JP 2006-87319 A), a method wherein a surfactant is fed at the stage of enzymatic saccharification to suppress enzyme adsorption and thereby enhance the recovery efficiency (JP 63-87994 A), a method wherein the residue produced by enzymatic saccharification is subjected to electric treatment to recover the enzyme component (JP 2008-206484 A) and a method wherein the residue produced by enzymatic saccharification is fed again to another batch of biomass and the enzymes is thereby reused (JP 55-144885 A).
Methods for producing sugar liquids by recovering/reusing enzyme have been developed as described above, but the effects of these methods have been insufficient in view of reduction in the amount of the enzyme used. Therefore, it could be helpful to provide a process wherein the effect of reducing the amount of enzyme is higher than those in the conventional methods.